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21英语教师网 > 备课资源 > 拓展阅读 > 正文
Deep sea secrets
作者:21ST    来源:高中版第167期    日期: 2010-03-31
人教版高二年级:Under the sea

关键词:Nature: animals and plants under the sea; legends of the sea

话题归类:自然Nature



你知道海水为什么是咸的吗?它会不会变淡或者变得更咸呢?


HAVE you ever noticed that, in the summer, when your sweat dries it will leave marks on your T-shirt? The marks are tiny bits of salt.

If you go to the seaside, you will know that seawater does the same to your clothes, because it also has a lot of salt in it.

Water evaporates from the surface of the sea but the salt remains. Have you ever thought about whether the seas will keep getting saltier? The answer is no. The oceans have stayed at about 3.5 per cent salt content for hundreds of millions years. It maintains a constant level of salt in different ways.

Pick up a clamshell (蛤壳) and weigh it in your hand. It is heavy. All creatures need sodium (钠) to live and most need calcium to build bones and shells. The clam, like all sea creatures, gets its sodium and calcium from seawater. When creatures die, their salt is locked up in bones and shells, which drop to the bottom of the sea.

Reactions between seawater and rocks are not just one way. Sea salt not only dissolves from rocks, it also reacts with the rocks of the ocean crust (地壳) and volcanic lava (熔岩). The reactions take some of the salts in seawater away from the sea.

The outer hard crust of Earth is made up of a dozen or so hard plates that drift on extremely hot, soft rock like floating islands on a sea. The heat within Earth is not the same everywhere and the plates move due to the heat.

When an ocean plate bumps into a land plate, the less dense land plate floats over the ocean one. The ocean floor gets pushed under, and its salty rocks, along with shells and bones, are lost deep within Earth.

So, that's why the seas are salty but don't get any saltier.

HELP
reaction n. 反应
dissolve v. 溶解
bump into 撞击



Why is sea water salty?


Many minerals like sodium, calcium and magnesium (镁) are found on the surface of Earth. Every time it rains, tiny amounts of these mineral

are carried into rivers, and finally to the seas, along with rainwater. The two most common elements (元素) in sea water are sodium and calcium. These combine to form salt, making the sea water salty.


That's the simple picture, which is true but incomplete.

Sea water also picks up salt from the oceanic crust. The ocean floor has places where sea water goes very deep. There it can be heated by hot rocks,

and so can dissolve salts from the crust. When it cools and flows back into the ocean it takes salt with it.


Salt is added to the sea when an undersea volcano erupts (喷发). Sea water, once again, dissolves salts from the lava.



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Classroom link for Senior 2, Unit 13 from Senior English textbook for China



关键词:人教版 高二 Under the sea 自然Nature







 

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